After biosynthesis within the fibroblast, a procollagen molecule is secreted into the extracellular space where it must undergo a series of very ordered, time sensitive, and location sensitive sequential post-synthetic processing steps in order to become a mature cross-linked insoluble structural collagen fibril. We hypothesized that one fundamental independent mechanism by which chronic pressure overload (PO) increases myocardial fibrillar collagen content, causes the development of abnormal diastolic function and chronic heart failure is an alteration in post-synthetic procollagen processing. This overall hypothesis will be tested using 2 specific aims. Specific Aim 1: determine whether PO changes the balance between procollagen processing into mature cross-linked collagen fibrils vs. procollagen degradation. Specific Aim 2: determine in vitro, using murine primary cardiac fibroblast culture studies, whether a change in SPARC (Secreted Protein Acidic and Rich in Cysteine) expression or procollagen binding results in an isolated change in procollagen processing and fibrillar collagen deposition. PO will be produced by transverse aortic constriction (TAC) in mice. We will examine LV structure &function with echocardiography & catheterization, myocardial function with isolated papillary muscles studies, collagen content, composition and morphometric structure with histology &biochemistry, and procollagen synthesis, procollagen processing, and fibrillar collagen degradation rates with metabolic 14C and 3H proline labeling techniques. The mechanism by which TAC and SPARC alter post-synthetic procollagen processing will be examined using in vitro primary cardiac fibroblast culture studies. Thus, this project will examine whether alteration in SPARC-dependent procollagen processing is a fundamental mechanism by which PO increases myocardial fibrillar collagen content and causes diastolic dysfunction.